It is a desirable feature for cameras such as "Advanced Photographic System Cameras" (APS cameras) to have a MRI mode so that film cartridges may be removed from a camera with some frames exposed and other frames unexposed, and then later, reloaded to expose additional frames. By providing such a feature, customers may shoot a certain number of frames for a specific subject, rewind the film and then perhaps insert another film cartridge, and at a subsequent time reinsert the first cartridge. The customer, of course, wishes to take photographs with film remaining in the previously exposed cartridge and, therefore, must start with the first unexposed frame.
In APS cameras having magnetic read/write heads, the camera reads magnetic tracks on exposed film frames until it encounters the first available unexposed frame. The camera then performs a partial rewind of the film in order to pull the unexposed frame back past the beginning of the film gate. The camera then advances the unexposed frame through the film gate in a normal manner and registers the unexposed frame for the next photograph.
To perform this function in a small, low cost camera is difficult because the simple clutch arrangements inherent in low cost systems do not readily accommodate the MRI function. The MRI function usually utilizes planetary gear clutches, such as is disclosed in Japanese Kokai 2-87864, or ratchet type, over-running clutches such as is disclosed in U.S. Pat. No. 4,855,773, assigned to the assignee of the present invention. With these arrangements, the supply clutch is totally disengaged from its rewind function before the take-up clutch is allowed to engage, otherwise, gear train lock-up occurs. Accordingly, a delay action is required before the take-up clutch engages in order to ensure that the supply clutch is properly disengaged.
In more expensive systems, perhaps exemplified by U.S. Pat. No. 5,172,148, a second motor is utilized. With such a system, the MRI function is readily performed; however, employing of a second motor is expensive and, therefore, not a practical consideration for low cost cameras.
In view of the aforementioned considerations, there is a need for a low cost arrangement which would provide relatively inexpensive cameras with MRI capability so that, if the cameras are equipped with magnetic read-write heads, magnetic tracks on exposed films can be utilized to accomplish the MRI feature.